Method of manufacturing thrust plate, bearing device, method of manufacturing bearing device, and spindle motor

ABSTRACT

A heated tool is depressed onto the upper surface of a work in process piece made from a thermoplastic or thermosetting resin to deform the work in process piece, so that a concave portion is formed. In this way, a thrust plate with the concave portion can be manufactured easily and readily. By properly choosing a tool according to the radius of curvature of the lower end of a shaft, a concave portion having an appropriate radius of curvature can be formed on the work in process piece, and a thrust plate with high wear resistance can be manufactured.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a thrust plate for use in a bearing device, a bearing device including the thrust plate manufactured by the manufacturing method, a method of manufacturing a bearing device, and a spindle motor including the bearing device manufactured by the manufacturing method.

2. Description of the Related Art

A spindle motor for rotating magnetic data storage medium is mounted in a hard disk drive used in, e.g., personal computers and car navigation systems. In the spindle motor, a rotor unit is rotated relative to a stator unit with a bearing interposed therebetween.

The bearing includes a radial bearing part supporting a shaft in a radial direction and a thrust bearing part supporting the shaft in an axial direction. The radial bearing part is configured, e.g., within a gap between the shaft and a sleeve having a bearing hole that passes the shaft therethrough. Hydrodynamic pressure is produced in lubricant retained in the gap, and the shaft is thereby supported.

The thrust bearing part is configured by, e.g., a disc-shaped thrust plate and an end of the shaft which makes contact with the thrust plate. The shaft is supported in the axial direction with the end of the shaft contacted with one of the surfaces of the thrust plate.

If a bearing with a thrust plate, however, is used for an extended period of time, the top surface of the thrust plate becomes worn due to the sliding contact between one of the surfaces of the thrust plate and the shaft, sometimes leading to deviation of the shaft in the axial direction. The deviation of the shaft in the axial direction causes the deviation of the data storage medium in the axial direction, which may adversely affect the reliability of information read/write operation on the data storage medium.

To prevent such wear of the thrust plate, it is desirable that a concave curved surface with a suitable curvature be formed in advance on one of the surfaces of the thrust plate, and that the shaft be supported on the concave curved surface. The formation of such a concave curved surface on the thrust plate, however, entails increase in complexity of the manufacturing processes and rise in manufacturing cost.

SUMMARY OF THE INVENTION

An aspect of the present invention is directed to a method of manufacturing a thrust plate for use in a motor. The thrust plate configures a thrust bearing part with a shaft. The shaft has a convex curved surface on an end thereof and rotates around a central axis. An axially upper surface of the thrust plate comes into contact with the end of the shaft.

The method of manufacturing the thrust plate includes the following step a); that is, a plate-like work in process piece made from a thermoplastic or thermosetting resin is provided, and the upper surface of the work in process piece is heated and depressed with a member having a convex curved surface to form a concave curved surface on the work in process piece.

It should be noted that in the explanation of the present invention, when positional relationships among and orientations of the different components are described as being up/down or left/right, ultimately positional relationships and orientations that are in the drawings are indicated; positional relationships among and orientations of the components once having been assembled into an actual device are not indicated.

According to the present invention, the member having the convex curved surface may be depressed onto the one of the surfaces of the work in process piece made from a thermoplastic or thermosetting resin with the work in process piece being heated from the axially upper side, whereby the concave curved surface can be formed on the work in process piece. Accordingly, a thrust plate with a concave curved surface can be easily and readily manufactured. The concave curved surface formed on the thrust plate disperses the pressure applied from the shaft and reduces abrasion of the thrust plate.

Further, the concave curved surface may be formed on the upper surface of the work in process piece using a member having a convex curved surface with a larger radius of curvature than that of the end of the shaft; therefore, the radius of curvature of the concave curved surface of the resultant thrust plate is larger than the radius of curvature of the end of the shaft, so that the shaft can be supported on the thrust plate in a favorable manner.

Moreover, the member may be heated and then depressed on the upper surface of the work in process piece to heat the work in process piece from the upper side. Thus, the upper surface of the work in process piece can be easily heated.

Other features, elements, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a data storage medium drive taken along a plane including a central axis;

FIG. 2 is a cross-sectional view of a spindle motor taken along a plane including the central axis;

FIG. 3 is a cross-sectional view of a fluid dynamic bearing taken along a plane including the central axis;

FIG. 4 is a flowchart showing a procedure for manufacturing a thrust plate;

FIG. 5 illustrates a tool, a heating mechanism, and a work in process piece;

FIG. 6 illustrates the tool depressing the work in process piece;

FIG. 7 illustrates the tool being withdrawn from the work in process piece;

FIG. 8 is a flowchart showing a procedure for manufacturing the fluid dynamic bearing;

FIGS. 9 and 10 illustrate a work in process piece with a support member fixed thereto and the tool;

FIGS. 11 and 12 illustrate a work in process piece with a protective film formed thereon and the tool;

FIG. 13 is a cross-sectional view of a bearing in which the work in process piece and a cylindrical portion of a bearing housing are provided as a single member, taken along a plane including a central axis;

FIG. 14 is a flowchart showing a procedure for manufacturing a fluid dynamic bearing according to another embodiment;

FIG. 15 illustrates a concave portion being formed on the work in process piece inside the bearing housing;

FIG. 16 illustrates center alignment being performed on a sleeve and the tool using static pressure of compressed gas;

FIG. 17 illustrates center alignment being performed on the sleeve and the tool through contact of an elastic body;

FIG. 18 illustrates the tool being depressed while being rotated, onto the upper surface of the work in process piece;

FIG. 19 is a flowchart showing a procedure for manufacturing a fluid dynamic bearing according to another embodiment;

FIGS. 20 and 21 illustrate a gap being formed between a shaft and the sleeve simultaneously with the formation of the concave portion;

FIGS. 22 and 23 illustrate a gap being formed between the shaft and a seal member simultaneously with the formation of the concave portion;

FIG. 24 is a graph showing relationships between temperature of the tool and depths of concave portions;

FIG. 25 is a graph showing relationships between depressing force of the tool against work in process pieces and depths of concave portions; and

FIG. 26 is a cross-sectional view of a thrust plate provided with a bulged portion surrounding the concave portion, taken along a plane including the central axis.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 through 26, preferred embodiments of the present invention will be described in detail. It should be noted that in the explanation of the present invention, when positional relationships among and orientations of the different components are described as being up/down or left/right, ultimately positional relationships and orientations that are in the drawings are indicated; positional relationships among and orientations of the components once having been assembled into an actual device are not indicated. Meanwhile, in the following description, an axial direction indicates a direction parallel to a rotation axis, and a radial direction indicates a direction perpendicular to the rotation axis.

FIG. 1 is a cross-sectional view of a data storage medium drive 2 including a bearing device 5 according to a first preferred embodiment of the present invention, taken along a plane including a central axis. The data storage medium drive 2 is preferably a hard disk drive that performs information reading/writing while rotating a magnetic storage medium. As shown in FIG. 1, the data storage medium drive 2 preferably includes a housing 21, the storage medium, a spindle motor 1, and an access part 23.

The housing 21 preferably includes a substantially cup-shaped first housing member 211 and a plate-like second housing member 212. The first housing member 211 preferably includes an opening at its upper portion. Also, the spindle motor 1 and the access part 23 are disposed preferably at the inner bottom surface of the first housing member 211. The second housing member 212 is preferably joined to the first housing member 211 so as to close the opening at the upper portion of the first housing member 211. The storage medium, the spindle motor 1, and the access part 23 are contained in an internal space 213 of the housing 21 enclosed with the first housing member 211 and the second housing member 212. The internal space 213 of the housing 21 is an almost dustless clean space.

The storage medium 22 is preferably a substantially disc-shaped information recording medium with a hole at the center. The storage medium 22 is preferably loaded on a hub member 42 of the spindle motor 1 so as to be rotatably supported on the spindle motor 1. The access part 23 preferably includes a head 231, an arm 232, and a head moving mechanism 233. The head 231 is preferably brought in proximity to the main surface of the storage medium 22 to magnetically read and write information from and to the storage medium 22. The arm 232 preferably moves near the main surface of the storage medium 22 while supporting the head 231. The head moving mechanism 233 is arranged at a side of the storage medium 22. The head moving mechanism 233 moves the arm 232 so as to move the head 231 relative to the storage medium 22.

In this manner, the head 231 accesses a necessary position over the rotating storage medium 22 so as to read and write information from and into the storage medium 22. The head 231 may only either read or write information with respect to the storage medium 22.

Next, the configuration of the spindle motor 1 is detailed. FIG. 2 is a cross-sectional view of the spindle motor 1 taken along a plane including the central axis. As shown in FIG. 2, the spindle motor 1 preferably includes a stator unit 3 and a rotor unit 4. The stator unit 3 is preferably fixed to the housing 21 of the data storage medium drive 2. The rotor unit 4 preferably rotates around a central axis L with the storage medium 22 loaded thereon.

The stator unit 3 preferably includes a base member 31, a stator core 32, coils 33, and a bearing unit 34.

The base member 31 is preferably made of a metal material such as aluminum and is fixed to the housing 21 of the data storage medium drive 2 with screws or the like. The base member 31 is preferably provided with a substantially cylindrical holder part 311 that protrudes in an axial direction (a direction along the central axis L; the same holds true in the following description) to encircle the central axis L.

A through hole for holding the bearing unit 34 is preferably provided at the inner peripheral side (the inner peripheral side relative to the central axis L; the same holds true in the following description) of the holder part 311. The surface on the outer peripheral side (the outer peripheral side relative to the central axis L; the same holds true in the following description) of the holder part 311 preferably serves as an attachment surface to fit the stator core 32 in.

Although the base member 31 and the first housing member 211 are provided as separate members in the present embodiment, the base member 31 and the first housing member 211 may be provided as a single member. In this case, the holder part 311 is preferably provided in a member comprising both the base member 31 and the first housing member 211.

The stator core 32 preferably includes a core back 321 and a plurality of teeth 322. The core back 321 is preferably fixed to the outer peripheral surface of the holder part 311. The teeth 322 extend radially outward from the core back 321. The stator core 32 is formed of, e.g., magnetic steel sheets laminated in the axial direction.

The coils 33 are preferably formed of conductive wires wound around each of the teeth 322 of the stator core 32. The coils 33 are preferably connected to a predetermined power source device (not shown). The power source device applies a drive current through the coils 33, and magnetic fluxes are generated in a radial direction over the teeth 322. The magnetic fluxes generated at the teeth 322 interact with magnetic fluxes over a rotor magnet 43 (described later) so as to produce torque for rotating the rotor unit 4 around the central axis L.

The bearing unit 34 preferably supports a shaft 41 pertaining to the rotor unit 4 such that the shaft 41 is rotatable relative thereto. The bearing unit 34 configures a fluid dynamic bearing 5 with the shaft 41. It is to be noted that the bearing device in the present embodiment refers to a fluid dynamic bearing. FIG. 3 is an enlarged cross-sectional view showing a structure of the fluid dynamic bearing 5 taken along a plane including the central axis. As shown in FIG. 3, the bearing unit 34 preferably includes a sleeve 341, a thrust plate 342, a seal member 343, and a bearing housing 344.

The sleeve 341 preferably includes a substantially cylindrical shape and includes a bearing hole 341 a to receive the shaft 41. The sleeve 341 is preferably fixed to the inner peripheral surface of the bearing housing 344. A radial dynamic pressure bearing part is configured within a gap between the outer peripheral surface of the shaft 41 and the inner peripheral surface of the sleeve 341, which bearing part produces hydrodynamic pressure in lubricant retained in the gap during the rotation of the motor 1.

The inner peripheral surface of the sleeve 341 and the outer peripheral surface of the shaft 41 preferably oppose each other via a minute gap (e.g., a gap on the order of several μm) therebetween, in which lubricant 51 (described later) is arranged. The sleeve 341 is preferably formed of a sintered compact prepared by combining and solidifying a metal powder over heat. Thus, the sleeve 341 is preferably formed of a porous body including numerous minute cavities when observed microscopically, and the porous body contains lubricant. The shaft 41 slides in a favorable manner relative to the sleeve 341 impregnated with the lubricant. Additionally, the sleeve 341 of a sintered compact is available at relatively low cost.

The thrust plate 342 is preferably a substantially disc-shaped member disposed under the shaft 41. The thrust plate 342 preferably allows the lower end 41 b of the shaft 41 to contact the upper surface thereof, so as to support the shaft 41 axially while permitting the shaft 41 to rotate around the central axis L. The lower end 41 b of the shaft 41 and the thrust plate 342 configure a thrust bearing part.

A concave portion 342 a forming a concave curved surface (partly spherical shape) is preferably provided in a central portion on the upper surface of the thrust plate 342. The radius of curvature of the concave portion 342 a is preferably set equal to or larger than the radius of curvature of the lower end 41 b of the shaft 41; therefore, the upper surface of the concave portion 342 a point-contacts or plane-contacts the lower end 41 b of the shaft 41, whereby a pivot bearing part, which is a thrust bearing part, is configured between the thrust plate 342 and the shaft 41.

The shaft 41 is preferably capable of rotating around the central axis L at the pivot bearing part with extremely small rotational resistance. The concave portion 342 a provided on the thrust plate 342 preferably disperses the pressure from the shaft 41 to the thrust plate 342 so as to reduce abrasion on the upper surface of the thrust plate 342.

The thrust plate 342 is preferably made from a thermoplastic resin such as a polyacetal or a nylon and manufactured through a manufacturing method (described later). In addition, usable thermoplastic resins preferably include a polyamide-imide (PAI), a polyether ether ketone (PEEK), a thermoplastic polyimide (TPI), a polytetrafluoroethylene (PTFE), a polyphenylene sulfide (PPS), and a polybutylene terephthalate (PBT).

The thrust plate 342 however need not necessarily be made only of a thermoplastic resin. For example, a mixture containing a thermoplastic resin may be used, or a filler for improving abrasion resistance may be blended. Exemplary usable fillers include carbon fiber, carbon nanotube, carbon powder, graphite, glass fiber, and potassium titanate.

The seal member 343 is preferably a substantially annular member disposed on the sleeve 341. The inner peripheral surface 343 a of the seal member 343 is preferably provided with a sloping surface whose inner diameter increases toward the upper side. Thus, a gap 343 b between the inner peripheral surface 343 a of the seal member 343 and the outer peripheral surface of the shaft 41 increases in width toward the upper side.

An interface of the lubricant 51 in the gap 343 b preferably forms a meniscus due to surface tension. This structure minimizes the lubricant 51 from leaking out of the bearing unit 34. That is, a tapered seal is formed in the gap 343 b between the seal member 343 and the shaft 41. The seal member 343 is preferably made of a metal such as stainless steel or aluminum, or a resin. In addition, the seal member 343 and the sleeve 341 may be formed into a single member.

The bearing housing 344 is preferably a bottomed and substantially cylindrical member to contain the sleeve 341, the thrust plate 342, and the seal member 343 therein. The bearing housing 344 is preferably fixed inside the through hole provided at the inner peripheral side of the holder part 311 of the base member 31, preferably through press fitting or shrink fitting.

The sleeve 341 and the seal member 343 are preferably fixed onto the inner peripheral surface of the bearing housing 344, and the thrust plate 342 is disposed on the bottom surface inside the bearing housing 344. The bearing housing 344 is made such that, e.g., a galvanized sheet iron (SECE according to the JIS standard), which is formed by plating zinc over surfaces of a cold reduced carbon steel sheet (SPCC, SPCD, SPCE, according to the JIS standard), is pressed into a bottomed and substantially cylindrical shape.

The inside of the bearing housing 344 is preferably filled with the lubricant 51 preferably primarily containing ester. An oil primarily containing ester, such as a polyol ester oil or a diester oil, is used for the lubricant 51. Having good abrasion resistance, heat stability, and fluidity, oils primarily containing ester are suitable as the lubricant 51 for the fluid dynamic bearing 5.

The lubricant 51 is preferably filled uninterruptedly not only in the gap between the sleeve 341 and the shaft 41 but also in the gap between the thrust plate 342 and the bearing housing 344 and in the gap locally formed between the sleeve 341 and the bearing housing 344. That is, an entire internal space in the bearing housing 344 is filled with the lubricant 51.

Returning to FIG. 2, the rotor unit 4 preferably includes the shaft 41, the hub member 42, and the rotor magnet 43.

The shaft 41 is preferably a substantially columnar member provided along the central axis L. The shaft 41 is preferably supported in the bearing unit 34 with its lower portion received within the bearing hole 341 a of the sleeve 341 so as to rotate around the central axis L. Arrays 41 a of herringbone radial dynamic pressure grooves are preferably provided on the outer peripheral surface of the shaft 41, which arrays 41 a develop hydrodynamic pressure in the lubricant 51 filled between the outer peripheral surface of the shaft 41 and the inner peripheral surface of the sleeve 341.

As the shaft 41 rotates, the arrays 41 a of radial dynamic pressure grooves preferably apply pressure onto the lubricant 51 to cause the lubricant 51 to act as a working fluid so that the shaft 41 is supported radially while rotating. The arrays 41 a of radial dynamic pressure grooves may be provided on the inner peripheral surface of the sleeve 341.

In the vicinity of the lower end of the shaft 41 fixed is a flange member 411 to keep the shaft 41 from slipping out of the bearing unit 34. The flange member 411 is preferably integrated with the shaft 41 to provide a projection projecting radially from the outer peripheral surface of the shaft 41.

The upper surface of the flange member 411 axially opposes the lower surface of the sleeve 341. When an upward force acts on the rotor unit 4, the upper surface of the flange member 411 touches the lower surface of the sleeve 341, whereby the stator unit 3 and the rotor unit 4 are prevented from being separated from each other. The shaft 41 and the flange member 411 may be provided as a single member.

The lower end 41 b of the shaft 41 preferably forms a convex curved surface (spherical shape) and protrudes more to the lower side than the flange member 411. The lower end 41 b of the shaft 41 preferably makes contact with the concave portion 342 a (see FIG. 3) of the thrust plate 342, whereby the shaft 41 is supported axially.

The hub member 42 is preferably fixed to the shaft 41 and rotates with the shaft 41. The hub member 42 preferably has such a shape as to stretch out radially around the central axis L. More specifically, the hub member 42 includes a joined portion 421, a barrel portion 422, and a hanging portion 423.

The joined portion 421 is preferably joined to an upper end portion of the shaft 41, preferably through press fitting or shrink fitting. The barrel portion 422 preferably expands radially outward and axially downward from the joined portion 421. The hanging portion 423 preferably hangs from the outer peripheral edge of the barrel portion 422. The hub member 42 covers over the stator core 32, the coils 33, and the bearing unit 34.

The barrel portion 422 of the hub member 42 is preferably provided with a first supporting surface 422 a and a second supporting surface 422 b so as to support the storage medium 22. The first supporting surface 422 a preferably forms a plane extending perpendicularly to the central axis L. The second supporting surface 422 b is a cylindrical surface provided in parallel to the central axis L, at the inner peripheral side of the first supporting surface 422 a.

When the storage medium 22 is loaded on the hub member 42, the lower surface of the storage medium 22 meets the first supporting surface 422 a while the inner peripheral portion (the inner peripheral surface or the inner peripheral edge) of the storage medium 22 meets the second supporting surface 422 b, whereby the storage medium 22 is supported horizontally. The hub member 42 is preferably formed from a metal material such as aluminum or an aluminum alloy, a ferromagnetic stainless steel, or a cold-reduced carbon steel sheet (SPCC, SPCD, SPCE).

The rotor magnet 43 is preferably fixed on the inner peripheral surface of the hanging portion 423 of the hub member 42. The rotor magnet 43 is preferably disposed annularly to surround the central axis L. A pole face is preferably formed on the inner peripheral surface of the rotor magnet 43 to oppose the outer peripheral surfaces of the teeth 322 of the stator core 32.

In such a spindle motor 1, radial magnetic fluxes are generated over the teeth 322 of the stator core 32 upon application of a drive current through the coils 33 of the stator unit 3. Then, interaction of magnetic fluxes between the teeth 322 and the rotor magnet 43 develops torque to cause the rotor unit 4 to rotate around the central axis L relative to the stator unit 3. The storage medium 22 supported on the hub member 42 preferably rotates around the central axis L together with the shaft 41 and the hub member 42.

Next, a description is made on a procedure for manufacturing the thrust plate 342 and the fluid dynamic bearing 5 that constitute part of the above-described spindle motor 1. FIG. 4 is a flowchart showing a procedure for manufacturing the thrust plate 342. To manufacture the thrust plate 342, as shown in FIG. 4, a work in process piece 342 p to be a base material of the thrust plate is provided (step S11). The work in process piece 342 p is preferably a substantially disc-shaped member of a thermoplastic resin such as a polyacetal or a nylon, with a thickness of, e.g., about 0.5 mm.

Subsequently provided is a tool 60 for forming the concave portion 342 a on the upper surface of the work in process piece 342 p. The tool 60 may be, e.g., a metal member that is higher in softening temperature than the work in process piece 342 p. As shown in FIG. 5, the tool 60 has preferably a substantially columnar shape with the lower end 60 a thereof having a convex curved surface (partly spherical shape) that corresponds to the curved surface shape of the concave portion 342 a to be formed on the upper surface of the work in process piece 342 p.

The lower end 60 a of the tool 60 in a non-operating state is preferably inserted into a predetermined heating mechanism 71 and heated to a predetermined temperature by the heating mechanism 71 (step S12).

The heating mechanism 71 may be constructed using various heating devices such as a high frequency induction heater or a hot plate. The tool 60, the heating mechanism 71, and a driving mechanism (not shown) for moving the tool 60 may be coupled to one another into a single heating apparatus.

After heating the lower end 60 a of the tool 60 sufficiently in the heating mechanism 71, as shown in FIG. 5, the tool 60 is taken out from the heating mechanism 71 and disposed above the work in process piece 342 p. Then, as shown in FIG. 6, the tool 60 is lowered along the central axis L until the lower end 60 a thereof touches a central portion on the upper surface of the work in process piece 342 p, whereupon the lower end of the tool 60 is depressed onto the upper surface of the work in process piece 342 p (step S13). After duration of depression for a predetermined period of time, as shown in FIG. 7, the tool 60 is withdrawn from the work in process piece 342 p.

In step S13 above, the upper surface of the work in process piece 342 p becomes softened and deformed by being applied with the heat accumulated in the lower end 60 a of the tool 60 and the depressing force from the tool 60. The shape of the lower end 60 a of the tool 60 is thereby transferred to the upper surface of the work in process piece 342 p. In this manner, a concave portion 342 a in the shape of a concave curved surface is formed on the upper surface of the work in process piece 342 p. Thus, the work in process piece 342 p provided with the concave portion 342 a is ready for use as the thrust plate 342.

As described above, in the present embodiment, the heated tool 60 is depressed onto the upper surface of the work in process piece 342 p made from a thermoplastic resin and softens and deforms the work in process piece 342 p, so that the concave portion 342 a is formed. The thrust plate 342 with the concave portion 342 a can thus be manufactured easily and readily.

In the above-described steps S12 and S13, it is possible to use a tool 60 having a convex curved surface with a radius of curvature which is substantially equal to or larger than the radius of curvature of the lower end 41 b of the shaft 41. By doing so, the radius of curvature of the concave portion 342 a which is formed on the upper surface of the work in process piece 342 p is also made substantially equal to or larger than the radius of curvature of the lower end 41 b of the shaft 41.

As a result, the shaft 41 can be supported in a favorable manner on the concave portion 342 a provided on the upper surface of the thrust plate 342. The radius of curvature of the lower end 60 a of the used tool 60 is determinative of the radius of curvature of the concave portion 342 a. For this reason, by properly choosing the tool 60 according to the radius of curvature of the lower end 41 b of the shaft 41, the concave portion 342 a with a suitable radius of curvature can be formed on the work in process piece 342 p. A thrust plate 342 highly resistant to abrasion can therefore be manufactured.

FIG. 8 is a flowchart showing a procedure for manufacturing the fluid dynamic bearing 5 using the thrust plate 342 manufactured through the foregoing procedure. To initiate the manufacture of the fluid dynamic bearing 5, the thrust plate 342 manufactured through the foregoing procedure is first inserted into the bearing housing 344 such that the thrust plate 342 is disposed on the upper surface of the bottom of the bearing housing 344 (step S21).

Subsequently, the shaft 41, the sleeve 341, and the seal member 343 are preferably sequentially fitted in the bearing housing 344 to dispose these members in predetermined positions, respectively, inside the bearing housing 344 (step S22). After that, the lubricant 51 is filled in the bearing housing 344 (step S23), whereupon the fluid dynamic bearing 5 is completed.

At a time of manufacturing the fluid dynamic bearing 5, the base member 31, the stator core 32, and the coils 33 that pertain to the stator unit 3 may be fitted to the bearing housing 344 beforehand. In addition, the hub member 42 and the rotor magnet 43 that pertain to the rotor unit 4 may be fitted to the shaft 41 beforehand. The method of fixing the sleeve 341 and the seal member 343 to the bearing housing 344 may include various methods such as insertion, press fitting, and caulking.

Another preferred embodiment of the present invention is described below with reference to FIGS. 13 to 17.

Although in the foregoing embodiment, the concave portion 342 a is formed on the upper surface of the work in process piece 342 p outside the bearing housing 344, the present invention is not limited thereto. For instance, the concave portion 342 a may be formed on the upper surface of the work in process piece 342 p in such a manner that the work in process piece 342 p is first disposed in the bearing housing 344, followed by the insertion of the tool 60 into the bearing housing 344. That is, the bottom of the bearing housing may be provided for the thrust plate, in other words, the bottom of the bearing housing is the thrust plate. With this structure, there is no need to provide a space for disposing the work in process piece 342 p outside the bearing housing 344, and the manufacturing process of the fluid dynamic bearing 5 can be further simplified.

Particularly, in the case where the bearing housing 344 and the work in process piece 342 p are integrated with each other beforehand, like, e.g., a fluid dynamic bearing 6 shown in FIG. 13, the work in process piece 342 p and a cylindrical portion 344 a of the bearing housing 344 are preferably constructed into a seamless single member made from a thermoplastic or thermosetting resin. In this case, the concave portion 342 a may be formed on the upper surface of the work in process piece 342 p by inserting the tool 60 into the bearing housing 344.

A procedure for manufacturing a fluid dynamic bearing in such a case is described by way of example with reference to the flowchart of FIG. 14. Provided first preferably is a bearing housing 344 in which the work in process piece 342 p is disposed beforehand, or a bearing housing 344 integrated with the work in process piece 342 p into a single member (step S31). Then, the sleeve 341 is preferably disposed in a predetermined position in the bearing housing 344 provided as above (step S32).

The lower end 60 a of the tool 60 is heated in a heating mechanism 71 that is similar to the one used in the foregoing embodiment (step S33). Then, as shown in FIG. 15, the tool 60 is inserted from the opening at the upper portion of the bearing housing 344 through the bearing hole 341 a of the sleeve 341 disposed within the bearing housing 344, and the lower end 60 a of the tool 60 is depressed onto a substantially central portion on the upper surface of the work in process piece 342 p (step S34).

After that, the tool 60 is taken out from the bearing housing 344, and the shaft 41 and the seal member 343 are sequentially disposed in predetermined positions in the bearing housing 344 (step S35). Finally, the lubricant 51 is filled within the bearing housing 344 (step S36), so that a fluid dynamic bearing is provided.

In the case where the tool 60 is inserted through the bearing hole 341 a of the sleeve 341, as shown in FIG. 15, it is preferred that a heat accumulating part 60 b is provided only in the vicinity of the substantially central portion out of the entire lower end 60 a of the tool 60 to prevent heat from being accumulated in the circumferential edge portion of the tool 60. In this manner, thermal influence of the tool 60 on the sleeve 341 can be suppressed. Also, at least the outer peripheral surface of the tool 60 is desirably made of a material lower in hardness than the inner peripheral surface of the sleeve 341. In this manner, it is possible to protect the sleeve 341 from being damaged when the tool 60 touches the sleeve 341.

In the case where the tool 60 is inserted through the bearing hole 341 a of the sleeve 341, it is preferred that the position of the tool 60 is adjusted relative to the sleeve 341 so that the central axes of the sleeve 341 and of the tool 60 are aligned to be substantially coincident with each other. Then, preferably with the central axes of the sleeve 341 and of the tool 60 aligned, the lower end 60 a of the tool 60 is brought into contact with the upper surface of the work in process piece 342 p.

In this manner, the shaft 41 which is supported by the sleeve 341 and the concave portion 342 a which is provided on the work in process piece 342 p are preferably substantially aligned along their central axes. Accordingly, it is possible to prevent generation of such wear as to be caused by the thrust plate 342 moving to one side in the radial direction, with the result of improved rotational accuracy of the shaft 41.

Specifically, e.g., as shown in FIG. 16, a plurality of openings 60 c are preferably provided in the outer peripheral surface of the tool 60, and center alignment of the tool 60 with respect to the sleeve 341 may be performed by means of the static pressure of compressed gas that is discharged from the openings 60 c. The openings 60 c are preferably provided along a circumferential direction at substantially equal intervals on the outer peripheral surface of the tool 60 such that each opening 60 c opens to the radially outer side.

Additionally, as shown in FIG. 17, the outer peripheral surface of the tool 60 is covered with an elastic body 61 having a substantially uniform circumferential thickness. Then, by inserting the tool 60 through the bearing hole 341 a of the sleeve 341 while keeping the outer peripheral surface of the elastic body 61 in contact with the inner peripheral surface of the sleeve 341, the sleeve 341 and the tool 60 may be aligned with each other.

In this manner, the elastic body 61 in a contracting state meets the inner peripheral surface of the sleeve 341, so that the tool 60 is supported with pressure being applied uniformly to the tool 60 from the outer peripheral side; therefore, the sleeve 341 and the tool 60 can be aligned with each other in a favorable manner. In order to protect the sleeve 341 from damage, the elastic body 61 is preferably made from a material lower in hardness than the sleeve 341.

Still another preferred embodiment of the present invention is described below with reference to FIGS. 19 to 23.

In the foregoing embodiments, the concave portion 342 a is formed on the upper surface of the work in process piece 342 p using the tool 60 which is not a constituent member of the fluid dynamic bearing 5, but the present invention is not limited thereto. For instance, the concave portion 342 a may be formed on the upper surface of the work in process piece 342 p using the shaft 41 which constitutes part of the fluid dynamic bearing 5. A manufacturing procedure in such a case is described by way of example with reference to the flowchart of FIG. 19.

As in step S11 in the foregoing embodiment, a work in process piece 342 p made from a thermoplastic or thermosetting resin is first provided (step S41). Also, the lower end 41 b of the shaft 41 is heated using a heating mechanism 71 similar to the one used in the foregoing embodiment (step S42). Subsequently, the work in process piece 342 p, the shaft 41, the sleeve 341, and the seal member 343 are sequentially disposed in predetermined positions within the bearing housing 344, respectively (step S43).

Then, the shaft 41 is slightly lowered along the central axis L to depress the lower end 41 b of the shaft 41 onto the upper surface of the work in process piece 342 p (step S44). The upper surface of the work in process piece 342 p is subjected to the heat accumulated in the lower end 41 b of the shaft 41 and the depressing force from the lower end 41 b to be softened and deformed. In this manner, a concave portion 342 a in the form of a concave curved surface is preferably formed on the upper surface of the work in process piece 342 p. As a result, the work in process piece 342 p provided with the concave portion 342 a functions as the thrust plate 342.

Since this configuration allows the concave portion 342 a to be formed on the upper surface of the work in process piece 342 p without the use of the tool 60, the thrust plate 342 and the fluid dynamic bearing 5 can be made even more easily at low cost. In addition, since the center of the shaft 41 and that of the concave portion 342 a can easily be brought into substantial coincidence on the central axis L, the thrust plate 342 can be favorably prevented from becoming worn eccentrically.

In the case where the concave portion 342 a is formed using the shaft 41 in the above-described manner, as shown in FIGS. 20 and 21, a gap D may be formed along the axial direction between the flange member 411 of the shaft 41 and the lower surface of the sleeve 341 simultaneously with the formation of the concave portion 342 a. Specifically, the amount of displacement of the shaft 41 in step S44 may be controlled to be substantially equal to the width of the gap D to be formed between the flange member 411 and the sleeve 341. In this manner, the step of forming the concave portion 342 a and the step of forming the gap D need not be performed individually, so that the manufacturing efficiency of the fluid dynamic bearing 5 can be further improved.

FIGS. 22 and 23 show still another fluid dynamic bearing 7. In this fluid dynamic bearing 7, a raised portion 343 c is formed on the inner peripheral side of the seal member 343, instead of the flange member 411. A stepped portion 41 c that is provided on the outer peripheral surface of the shaft 41 contacts the raised portion 343 c to prevent the shaft 41 from slipping out of the bearing unit 34.

Also in such a fluid dynamic bearing 7, the concave portion 342 a may be formed on the upper surface of the work in process piece 342 p using the shaft 41. As shown in FIGS. 22 and 23, a gap D may also be formed along the axial direction between the stepped portion 41 c of the shaft 41 and the raised portion 343 c of the seal member 343 simultaneously with the formation of the concave portion 342 a.

Another preferred embodiment of the present invention is described below with reference to FIGS. 24 and 25.

According to the present invention, advantages of the present invention can similarly be obtained from the thrust plate 342 manufactured by applying a manufacturing method equivalent to those of the foregoing embodiments to a work in process piece 342 p made from a thermosetting resin.

Exemplary thermosetting resins include a phenol resin and an epoxy resin. In order to improve wear resistance, it is also possible to use a thermosetting resin mixed with a filler such as carbon fiber, carbon nanotube, carbon powder, graphite, glass fiber, or potassium titanate.

Such thermosetting resins have better heat resistance than thermoplastic resins; therefore, the thrust plate 342 manufactured from a thermosetting resin is less liable to deformation even if frictional heat is generated between the lower end 41 b of the shaft 41 and the concave portion 342 a of the thrust plate 342 during operation of the spindle motor 1.

FIG. 24 is a graph showing relationships between temperature of the tool 60 and depths of resultant concave portions 342 a when the concave portions 342 a were formed by depressing the lower end 60 a of the heated tool 60 on the upper surfaces of a work in process piece 342 p made from a polyamide-imide (a thermoplastic resin) and of a work in process piece 342 p made from a phenol resin (a thermosetting resin). In the example shown in FIG. 24, depressing force of the tool 60 applied against each work in process piece 342 p was 250 N, and depression duration was fifteen seconds, with respect to both the work in process pieces 342 p.

Referring to the result shown in FIG. 24, although differences can be seen in the change curves for the case in which a work in process piece 342 p made from a polyamide-imide was used and for the case in which a work in process piece 342 p made from a phenol resin was used, it is indicated in both the cases that the depths of the concave portions 342 a formed on the work in process pieces 342 p increase with the increase in temperature of the tool 60.

Further, FIG. 25 is a graph showing relationships between the depressing force of the tool 60 applied against the work in process pieces 342 p and the depths of the resultant concave portions 342 a when the concave portions 342 a were formed by depressing the lower end 60 a of the heated tool 60 on the upper surfaces of a work in process piece 342 p made from a polyamide-imide (a thermoplastic resin) and of a work in process piece 342 p made from a phenol resin (a thermosetting resin).

In the example shown in FIG. 25, the temperature of the tool 60 was set to 100° C. for the work in process piece 342 p made from a polyamide-imide, while the temperature of the tool 60 was set to 150° C. for the work in process piece 342 p made from a phenol resin.

Referring to the result shown in FIG. 25, the depths of the concave portions 342 a formed on the work in process pieces 342 p increase with increase in depressing force of the tool 60 against the work in process pieces 342 p, in both the cases in which the work in process piece 342 p made from a polyamide-imide was used and in which the work in process piece 342 p made from a phenol resin was used.

That is, the results shown in FIGS. 24 and 25 show that a manufacturing method equivalent to those of the foregoing embodiments is applicable to the work in process piece 342 p made from a thermosetting resin such as a phenol resin. Moreover, it can be seen that the depth of the concave portion 342 a formed on the upper surface of the work in process piece 342 p can be controlled by adjusting the temperature of the tool 60 and the depressing force thereof applied against the work in process piece 342 p in either case of using a thermoplastic resin or of using a thermosetting resin.

The preferred embodiments of the present invention have been described above, but the present invention is not limited to the foregoing embodiments and can be modified in various ways. A variety of modifications of the present invention are described in the following description.

In the foregoing embodiments, the lower end 60 a of the tool 60 is heated to apply heat from the tool 60 onto the upper surface of the work in process piece 342 p; however, the present invention is not limited thereto, and the upper surface of the work in process piece 342 p may be heated through other methods. For instance, a heat source other than the tool 60 may be brought close to or into contact with the upper surface of the work in process piece 342 p to apply heat onto the upper surface of the work in process piece 342 p. It should be noted however that it is simpler to perform the process by applying heat and pressure onto the upper surface of the work in process piece 342 p with a single tool 60, in which case the heat and pressure can work on substantially the same position on the work in process piece 342 p.

In the foregoing embodiments, the tool 60 is contacted with the work in process piece 342 p, but the present invention is not limited thereto. A support member 342 q as shown in FIGS. 9 and 10 may be fixed on the lower surface of the work in process piece 342 p provided in step S11, and the lower end 60 a of the tool 60 may be thereafter contacted with the upper surface of the work in process piece 342 p. The support member 342 q may be made from a material higher in softening temperature and in hardness than the work in process piece 342 p, preferably from a metal. With this structure, it is possible to prevent the work in process piece 342 p from being deflected overall due to the heat and pressure applied in forming the concave portion 342 a. Particularly, even if the thickness of the work in process piece 342 p itself is small, or even if the work in process piece 342 p is made through insert molding where the support member 342 q is set within a mold, the concave portion 342 a can be formed in a favorable manner on the upper surface of the work in process piece 342 p.

As shown in FIGS. 9 and 10, the support member 342 q may be heated by connecting a heating mechanism 72 to the support member 342 q. Specifically, during or prior to the formation of the concave portion 342 a on the upper surface of the work in process piece 342 p, the support member 342 q may be heated to conduct the heat through the lower surface approximately up to the upper surface of the work in process piece 342 p. In this manner, an increased heat quantity can be applied in the vicinity of the upper surface of the work in process piece 342 p, which allows the concave portion 342 a to be formed even more easily.

Also, the work in process piece 342 p may be heated only from the lower surface side by heating the support member 342 q without heating the lower end 60 a of the tool 60. The heating mechanism 72 can be constructed using a variety of known heating devices such as a high frequency induction heater or a hot plate.

Moreover, a protective film 342 r as shown in FIGS. 11 and 12 may be formed over the upper surface of the work in process piece 342 p provided in step S11, and the lower end 60 a of the tool 60 may be thereafter contacted with the upper surface of the protective film 342 r. In this manner, the thrust plate 342 can be further protected from being worn due to the sliding contact with the shaft 41. Any protective film 342 r may be used as long as it is a coating layer higher in wear resistance than the thermoplastic or thermosetting resin forming the work in process piece 342 p. The preferable example of the protective film 342 r includes DLC (diamond-like carbon). It is also possible to form the concave portion 342 a first on the upper surface of the work in process piece 342 p and thereafter form the protective film 342 r over the upper surface of the work in process piece 342 p provided with the concave portion 342 a.

In the foregoing embodiments, the tool 60 is moved axially so that the tool 60 is depressed onto the upper surface of the work in process piece 342 p, thereby forming the concave portion 342 a on the upper surface of the work in process piece 342 p; however, the present invention is not limited thereto. For instance, as shown in FIG. 18, the tool 60 may be depressed onto the upper surface of the work in process piece 342 p while the tool 60 is being rotated with the central axis L at the rotational center.

In this manner, even if the center of the lower end 60 a of the tool 60 slightly deviates from the central axis L, the concave portion 342 a can be so formed on the upper surface of the work in process piece 342 p as to be rotationally symmetric with respect to the central axis L. Accordingly, it is possible to further curb the eccentric wear of the thrust plate 342 caused by the shaft 41 as well as to improve rotational accuracy of the shaft 41.

As shown in FIG. 26, when the concave portion 342 a is formed on the upper surface of the work in process piece 342 p down to a certain depth, a bulged portion 342 b is formed around the concave portion 342 a. Such a bulged portion 342 b formed around the concave portion 342 a (i.e., the concave portion 342 a formed to have such a depth that the bulged portion 342 b is formed) will surround the lower end 41 b of the shaft 41 when the lower end 41 b of the shaft 41 contacts the concave portion 342 a. This structure regulates relative movement of the shaft 41 and the thrust plate 342 in the radial direction, so that the lower end 41 b of the shaft 41 can be kept from going out of the thrust plate 342.

In the foregoing embodiments, the radial bearing part is configured by having the inner peripheral surface of the sleeve 341 and the outer peripheral surface of the shaft 41 oppose each other with the lubricant 51 filled therebetween, but the present invention is not limited thereto. For instance, the radial bearing part may be a sliding bearing in which the shaft and the sleeve contact each other.

In addition, an outer rotor motor with a rotatable shaft has been described in the foregoing embodiments, whereas the present invention is applicable to a motor in which the shaft is fixed to the base member or to an inner rotor motor.

Further, the above-described spindle motor 1 is used to rotate the magnetic storage medium 22, whereas the present invention is also applicable to motors for rotating other recording disks such as optical disks (i.e., data storage medium 22).

Moreover, the present invention may be appropriately combined with any technique described in the foregoing embodiments and in the plurality of modifications.

Furthermore, the bearing device is applicable not only to fluid dynamic bearings but also to sliding bearings in which the shaft and the sleeve contact each other without utilizing hydrodynamic pressure.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1. A method of manufacturing a thrust plate for use in a bearing device, the thrust plate having a thrust bearing part with a shaft, the shaft having a convex curved surface on an end thereof and rotating around a central axis, an axially upper surface of the thrust plate contacting the end of the shaft, the method comprising the step of: a) heating a plate-like work in process piece made from one of a thermoplastic resin and a thermosetting resin and depressing a member having a convex curved surface onto an upper surface of the work in process piece in such a manner as to form a downwardly-concave curved surface on the work in process piece, to provide the thrust plate.
 2. The manufacturing method according to claim 1, wherein a radius of curvature of the convex curved surface of the member is larger than a radius of curvature of the end of the shaft.
 3. The manufacturing method according to claim 1, wherein the end of the shaft is used as the member in the step a).
 4. The manufacturing method according to claim 1, wherein in the step a), the member is heated, and the work in process piece is heated by depressing the heated member onto the upper surface of the work in process piece.
 5. The manufacturing method according to claim 1, further comprising the step of prior to the heating of the work in process piece, fixing a support member onto a lower surface of the work in process piece, the support member being made of a material higher in softening temperature than the resin forming the work in process piece.
 6. The manufacturing method according to claim 1, further comprising the step of after the step a), forming a coating layer over the upper surface of the work in process piece, the coating layer being higher in wear resistance than the resin forming the work in process piece.
 7. The manufacturing method according to claim 1, wherein in the step a), the member is depressed onto the upper surface of the work in process piece while the member is being rotated around the central axis.
 8. The manufacturing method according to claim 1, wherein in the step a), a bulged portion is formed around the concave curved surface simultaneously with the formation of the concave curved surface on the work in process piece.
 9. A bearing device comprising the thrust plate manufactured by the manufacturing method according to claim
 1. 10. A method of manufacturing a thrust plate for use in a bearing device, the thrust plate configuring a thrust bearing part with a shaft, the shaft having a convex curved surface on an end thereof and rotating around a central axis, an axially upper surface of the thrust plate contacting the end of the shaft, the method comprising the steps of: a) fixing a support member on an axially lower surface of a plate-like work in process piece, the work in process piece being made from one of a thermoplastic resin and a thermosetting resin, the support member being made of a material higher in softening temperature than the resin forming the work in process piece; and b) depressing a member having a convex curved surface onto an upper surface of the work in process piece while heating the work in process piece in such a manner as to form a concave curved surface on the work in process piece, to provide the thrust plate.
 11. The manufacturing method according to claim 10, wherein a radius of curvature of the convex curved surface of the member is larger than a radius of curvature of the end of the shaft.
 12. The manufacturing method according to claim 10, wherein the end of the shaft is used as the member in the step b).
 13. The manufacturing method according to claim 10, wherein in the step b), the member is heated, and the work in process piece is heated by depressing the heated member onto the upper surface of the work in process piece.
 14. The manufacturing method according to claim 10, wherein in the step b), the support member is heated to conduct the heat of the support member from the support member through the lower surface of the work in process piece to the upper surface of the work in process piece.
 15. The manufacturing method according to claim 10, wherein in the step b), the member is depressed onto the upper surface of the work in process piece while the member is being rotated around the central axis.
 16. The manufacturing method according to claim 10, wherein in the step b), a bulged portion is formed around the concave curved surface simultaneously with the formation of the concave curved surface on the work in process piece.
 17. A bearing device comprising the thrust plate manufactured by the manufacturing method according to claim
 10. 18. A method of manufacturing a bearing device including a thrust bearing part supporting a shaft, the shaft having a convex curved surface on an end thereof and rotating around a central axis, the method comprising the steps of: a) disposing a substantially cylindrical sleeve having a bearing hole within a housing having its upper side opened and its lower side closed, the housing including a work in process piece made from one of a thermoplastic resin and a thermosetting resin at an axially lower side of the housing, and a cylindrical portion extending axially upward; b) inserting a member having a convex curved surface into the bearing hole from the upper side; c) after the step b), performing center alignment to determine relative positions between the member and the sleeve such that a central axis of the member and a central axis of the sleeve become substantially coincident with each other; and d) while performing the step c), depressing the member onto an upper surface of the work in process piece while heating the work in process piece in such a manner as to form a concave curved surface on the work in process piece, to provide a thrust plate.
 19. The manufacturing method according to claim 18, wherein in the step c), the center alignment is performed by feeding compressed gas into a minute gap between the member and the sleeve to raise pressure in the minute gap.
 20. The manufacturing method according to claim 19, wherein an opening is provided in an outer peripheral surface of the member such that the opening opens radially outward in the member, and in the step c), the compressed gas is fed through the opening of the member into the minute gap.
 21. The manufacturing method according to claim 18, wherein an outer peripheral surface of the member is made of a material lower in hardness than an inner peripheral surface of the sleeve.
 22. The manufacturing method according to claim 18, wherein an outer peripheral surface of the member is covered with an elastic body having a substantially uniform circumferential thickness, and in the step c), the center alignment is performed to determine the relative positions between the member and the sleeve, by bringing an outer peripheral surface of the elastic body into contact with an inner peripheral surface of the sleeve with the elastic body elastically deformed.
 23. The manufacturing method according to claim 18, wherein in the step d), the member is depressed onto the upper surface of the work in process piece while the member is being rotated around the central axis.
 24. The manufacturing method according to claim 18, wherein in the step d), the member is heated, and the work in process piece is heated by depressing the heated member onto the upper surface of the work in process piece to form the concave curved surface on the upper surface.
 25. The manufacturing method according to claim 18, wherein the end of the shaft is used as the member in the step d).
 26. The manufacturing method according to claim 25, wherein in the step d), a predetermined gap is formed axially between the shaft and a member disposed around the shaft simultaneously with the depression of the end of the shaft onto the upper surface of the work in process piece.
 27. The manufacturing method according to claim 18, wherein the housing includes a bottom at a lower side of the cylindrical portion, and the work in process piece is disposed on the bottom, in the bearing device manufactured by the manufacturing method according to claim
 18. 28. The manufacturing method according to claim 18, wherein the cylindrical portion and the work in process piece are provided as a seamless single member made from one of a thermoplastic resin and a thermosetting resin, and the concave curved surface is formed on the upper surface of the work in process piece.
 29. The manufacturing method according to claim 18, wherein in the step d), a bulged portion is formed around the concave curved surface simultaneously with the formation of the concave curved surface on the work in process piece.
 30. A spindle motor for driving a data storage medium by rotating the data storage medium, comprising: the bearing device manufactured by the manufacturing method according to claim 18; a stator unit including one of the shaft and the sleeve; and a rotor unit including a rotor magnet and the other of the shaft and the sleeve. 